True, classical thermodynamics projected its observations into a picture
of universal disarray at the end of time. Yet despite its cosmological
grandstanding, classical thermodynamics was the eminently practical science
behind the Industrial Revolution—the
mechanization of industry that began in England and went on to sweep
the world. The science of energy set forth universal pressure-volume-temperature
relationships that applied to everything from star systems and steam
engines to children's toys. It came up with the second law and coined
entropy, the mysterious quantity that inexorably increases as time
passes and heat disperses.
Thermodynamics began humbly enough. Its most important early observations
included how energy changes forms without disappearing—which became
the first law—and how the capacity for work inevitably is lost
to heat—basic to the second law.
These simple observations marked a major turning point in the history
of science. Sir Isaac Newton's physics described perfectly reversible
processes, like pendulums swinging and planets revolving around the sun.
But the cooling of objects and the burning of fuel were not perfect or
eternal like Newton's equations. They described irreversible
processes, imperfect processes marked by loss and marred by ultimate
failure. At first blush, the cosmos might seem to be a perpetual-motion
machine. In fact, in the real world, the pendulum stops swinging, and
its motive energy wanes. Over time, energy that might be used constructively
is sacrificed, apparently forever. A bent cigarette butt in an ashtray
does not straighten out, gather ash and suck smoke into itself, then
jump between the fingers of a man holding a burnt match that flares up
and develops a red tip, which he restores unscathed next to other matches
in a matchbook. Rather the reverse: Babies are born, cereal gets soggy,
desks get messy, and sideburns grow. Watches run down and people die.
Heat moves, without recompense, into the cool.
Thermodynamics had released the arrow of time. It went quivering into
Newton's shiny smooth apple, generating heat as friction. By and by,
perpetual-motion machines were realized to be an unworkable fantasy.
The past and future were different, and science could no longer ignore
it. Thermodynamics gave science a wake-up call, forced it to grapple
with the reality of linear time. But thermodynamics messed all that up.
It measured loss, and implied that—despite the magnificent motions
of the planets—time moves in only one direction. The direction
of burning.
Heat flowed "downhill," Carnot proposed, like a waterfall.
Just as taller waterfalls lead to more energy with which to turn waterwheels,
so larger temperature differentials (gradients) lead to more energy to
run steam engines. Carnot's likening heat's flow into the cool to the
fall of water over a precipice showed up the similarities between the
two processes, which could be harnessed, providing energy for work. Carnot
pointed out that it was not simply the temperature of the steam-producing
boiler that made pistons pump hard and fast in an engine, but rather
the difference between the temperatures of its hot boiler and
cooler radiator. "The production of heat is not sufficient to give
birth to the impelling power," Carnot wrote in his Réflexions
sur la puissance motrice du feu (Reflections on the motive force
of heat). "It is necessary that there should be cold; without it,
the heat would be useless" (Guillen 1995, 179). Without naming it
as such, Carnot had implicitly recognized the role of the temperature
gradient.
Heat alone, in other words, is not enough. It must flow—into
the cool. The difference across a distance—the gradient—is
what sets up the conditions for the flow to take place. The greater the
gradient, the more power to run the great machines of national pride.
Other things being equal, with steeper (but not too steep) gradients,
the energy-extraction potential increases.
Rudolf Clausius put a final touch on the edifice of classical thermodynamics
when he formalized his statement of the second law in 1850: "No
process is possible in which the sole result is the transfer of energy
from a cooler to a hotter body" (Atkins 1984, 25).
This statement is meaningful not only because it implies one-way time
is intrinsic to nature, but also because it does not rule out the adding
of energy to delay or reverse normal flows. And such events transpire.
One can, for example, use high-quality energy, say electricity, to run
a pump that carries water uphill. This may be tagged "unnatural." Nonetheless,
it does not violate the second law. If one were to allow the water to
run down the same hill through a generator to make electricity, it would
be impossible to capture all the potential energy, turn it into kinetic
energy, and then turn it into electricity to pump all the water back
up the hill. The effects of energy degradation can be delayed, but not
eluded.
Newton portrayed a universe in principle eternal, held together by unseen
gravity, running like celestial clockwork. Classical thermodynamics upset
the Newtonian applecart. Friction and entropy compromised would-be eternity,
compromised Earth's newly celestial nature. Earthly change was messier,
harder to measure, and more clearly irreversible than the arcs, cogs,
and wheels of the frictionless Newtonian solar system machine. Friction
and entropy introduced the element of time. To make matters worse, during
these same years in the nineteenth century when the rules of classical
thermodynamics were being hammered out, Darwin introduced his theory
of evolution, of biological complexity by natural selection. Eternity
beat a hasty retreat back to the mathematical imagination whence it came.
Clunk went the clockwork cosmos.
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